A SIMPLE HYDRODYNAMIC MODEL FOR THE LIQUID CIRCULATION VELOCITY IN A FULL-SCALE 2-PHASE AND 3-PHASE INTERNAL AIRLIFT REACTOR OPERATING IN THE GAS RECIRCULATION REGIME

For design purposes a simple model to predict the hydrodynamic behavio ur of a three-phase internal airlift reactor is developed. The model p redicts liquid circulation, gas hold-up and minimum gas supply rates f or solids suspension. The reactor type considered has an internal rise r and is not equipped with a gas disengagement area, resulting in a hi gh downcomer gas flow rate. Its purpose is waste water treatment using biofilm particles. First it is recognized that several flow regimes m ay be distinguished, necessitating different models. Modelling for the gas recirculation regime is straightforward based on the momentum bal ance combined with a simple assumption for the gas hold-up that is pos sible for these type of airlift reactors with unrestricted gas carryov er into the downcomer. The predictive model is compared successfully w ith a pilot-scale reactor (400 1) and a full-scale reactor (284 m(3), both with a draught tube height of about 12 m) containing up to 250 g/ l solid particles with superficial gas supply rates up to 0.1 m/s. (C) 1997 Elsevier Science Ltd.